For decades, plasticizers have been used for processing plastics, such as polyvinyl chloride. Recently, the requirements placed upon the plasticizers have become more stringent with respect to performance and non-toxicity to humans and the environment. One important requirement relates to minimum solution temperature and gel time. Solution temperature in the context of plasticizers is the temperature at which a homogeneous phase is formed from a polyvinyl chloride dispersion in a plasticizer (L. Meier: “Weichmacher” [“Plasticizers”], in R. Gächter, H. Müller (Ed.): Taschenbuch der Kunststoffadditive [Plastics additives handbook], 3rd Edition, pp. 361-362, Hanser Verlag, Munich 1990). Plasticizers with a low gel time permit fast processing that saves energy.
In the prior art, applications which require fast gelling use predominantly alkyl benzyl esters of aromatic polycarboxylic acids, an example being butyl benzyl phthalate (L. Meier: “Weichmacher” [“Plasticizers”], in R. Gächter, H. Müller (Ed.): Taschenbuch der Kunststoffadditive [Plastics additives handbook], 3rd Edition, p. 397, Hanser Verlag, Munich 1990).
However, the demands placed upon modern plasticizers include low volatility, as well as a low solution temperature. The volatility of plasticizers leads to undesired embrittlement, for example of flexible polyvinyl chloride, and also to pollution by what are known as volatile organic substances (VOCs), the intention being to avoid these in applications in close contact with consumers.
European Union Directive 2005/84/EC for phthalates imposes certain restrictions on the use of diisononyl phthalate (DINP), di(isodecyl)phthalate (DIDP), and di-n-octyl phthalate (DNOP) for the production of childrens' toys which have small parts. It also provides for a total ban on the use of di(2-ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP), and dibutyl phthalate (DBP) at concentrations greater than 0.1% for childrens' toys. Producers of PVC plasticizers reacted to this new Directive by developing phthalate-free alternatives, such as diisononyl hexahydrophthalate (Hexamoll® DINCH) from BASF AG. Other phthalate-free plasticizers are aryl alkylsulfonates (Mesamoll®, Lanxess Deutschland GmbH) or esters of benzoic acid (Benzoflex® grades, Velsicol Chemical Corp.), and these are in successful use.
However, many of these phthalate-free alternatives exhibit less-than-ideal property profiles, which accordingly can be improved for use as PVC plasticizers. A targeted change in the property profile of aryl alkylsulfonates, without impairing their favorable properties, is of great interest to their users. This can be achieved, for example, via use of small additions of additional components.
The object of the present invention consisted in finding phthalate-free plasticizer preparations which feature lower volatility than that of the individual components and which moreover have lower gel times than would be expected from a linear relationship between the individual components.
Surprisingly, it has now been found that phthalate-free plasticizer preparations of a mixture composed of at least one aryl alkylsulfonate and of at least one ester of benzoic acid with polyhydric alcohols exhibit such properties, as also do plasticizer preparations of a mixture composed of at least one aryl alkylsulfonate and of benzyl esters of polybasic aliphatic carboxylic acids, e.g. dibenzyl adipate.